This invention relates to an image forming system in which a plurality of image forming units are interconnected for forming images simultaneously.
A reader and a printer constituting a digital copier are capable of being utilized independently as an image reading device and an image output device, respectively. Accordingly, systems have been proposed in which the reader/printer is connected to an ordinary computer system using an external I/F interface so as to be utilized as an image input/output unit, or in which a plurality of sets of reader/printers are distributed and connected and a central control means for controlling them is provided to allow a high copy volume (CV) by using a plurality of printers simultaneously.
Further, with the recent improvements that have been made in the capabilities of color copiers and color printers, there is a greater possibility that these devices will be utilized unlawfully, as in counterfeiting. However, it has heretofore been impossible to specify, based upon the copy produced, the particular device used to make the copy or the individual who produced the copy. In order to prevent such unlawful copying, consideration has been given to registering data indicative of image patterns of specific originals in a color copier or color printer per se and forcibly inhibiting unlawful copying when the data is identified by an image recognition circuit.
However, the circuitry that discriminates specific originals is such that the number of image patterns capable of being registered is limited. This is disadvantageous in that it is impossible to register all types of specific originals. In addition, there are cases in which the circuitry for discriminating specific originals will not function in a color copier or color printer having an external interface.
For example, if the specifications of the image data in the external interface are such that data of the three primary colors red, green and blue are sent to the device simultaneously, the above-mentioned discriminating circuit will be capable of operating. However, if the data specifications have been made to conform to the individual characteristics of a printer, as in the case of data in the colors cyan, magenta, yellow and black, there will be a plurality of combinations capable of color reproduction. Consequently, a plurality of image patterns for discrimination are required and discrimination for detecting specific originals is very complicated. An additional drawback is a smaller number of images capable of being discriminated.
Furthermore, in a case where image data of each of the color components is sent to the device field-sequentially color by color, the image data must be accumulated in memory in order to discriminate an image. This leads to higher cost and necessitates a large expenditure for discriminating the specific images.
Even if the problem of the image signal from the external interface is solved and image recognition is performed by limiting the number of specific originals to the number capable of being recognized, erroneous recognition in which a picture quite similar to a registered specific original is discriminated as being the specific original or in which a soiled specific original is not discriminated as being the specific original cannot be avoided.
Accordingly, though it is important that the image forming device be provided with means for detecting specific originals, there is a limitation upon the number of specific originals that can be detected. Therefore, in a case where an original that is not supposed to be copied has been copied, specifying the copying machine or the individual that produced the copy is important.
With this as a background, a technique has been studied through which information capable of specifying the copying device or individual can be added on to a specific original. Specifically, this technique involves using an output color component (yellow, for example) that is least conspicuous to the human eye from among the output color components (magenta, cyan, yellow, black) of a copier, modulating the image signal of this color component (as by adding a constant value) and adding on a pattern representing the manufacturing serial number of the copying device.
Demand is great for the ability to output not only a reflective original but also images of a wide variety of kinds e.g., computer graphics (CG)!. Such a function is essential in modern digital copiers.
However, when system development in such a digital copier is considered, there is no correlation between the reader/printer actually used in copying and added-on information since the added-on information is not set appropriately. Such a copier makes it very difficult to specify, based upon the reproduced image, the copier that copied the image or the individual who performed the copying operation.
Further, when system development in such a digital copier is considered, one subject that arises is construction of a system in which high CV can be achieved by using a plurality of output devices simultaneously.
In a technique in which a plurality of reader/printer sets are connected and a central control unit is employed to control them, the number of sets of reader/printers capable of being connected must be determined when the constitution of the central control unit is considered. Limitations are encountered in terms of flexible system expansion according to need.